This invention relates to a disc brake and in particular guide pins for a disc brake that freely rotate in axial opening in ears on a caliper while sustaining a desired alignment between a caliper and a support member such that axial movement of the caliper is not impaired during a brake application and resistive torque developed during the brake application is essentially substantially transmitted into the support member through friction members rather than through the guide pins.
Disc brakes having first and second guide pins correspondingly retained in first and second bores in a support member that is fixed to the frame of a vehicle are known in the prior art. In such disc brakes, the support member receives the spaced apart first and second guide pins to allow the caliper to axially slide and allow corresponding first and second friction members to engage with a rotor and effect a brake application. The following U.S. Pat. Nos. 4,448,287; 4,958,703; 4,976,339; 5,526,904; 5,749,445; 5,810,122; 5,810,112; 5,819,884 5,934,416 may be considered typical of such disc brakes. Basically during a brake application, the first and second guide pins slide in the first and second bores in response to a reaction force developed by pressurized fluid being presented to an actuation chamber that acts on an actuation piston to directly move the first friction member toward a rotor. The caliper itself reacts to the reaction force by moving a second friction member toward and into engagement with the rotor during the brake application. On termination the presentation of pressurized fluid to the actuation chamber, the first and second friction members move away from the rotor to establish a running clearance. If either the first or second friction members do not move away from the-rotor brake drag occurs which can cause undesirable wear of either and both the friction members and rotor. It is known to utilize the resiliency of a seal associated with the actuation piston to assist in the moving the first friction member away from the rotor. Unfortunately, the second friction member is not directly moved away from the rotor but must rely on knock back by the rotor to eliminate brake drag. Brake manufacturers have attempted to reduce brake drag by developing low slide force calipers however the components of current disc brakes require tight tolerance to maintain desired operational capabilities. Unfortunately, if such tolerances are not maintained, a perpendicular relationship between the guide pins and rotor is not achieved and caming may occur that causes the guide pins to bind and result in an increase in the force required to move or slide the caliper with respect to the support member. In a review of the procedures employed in the manufacture of a disc brake, it was discovered when two piece guide pins were used caming could be introduced into the system during the attachment of a fixing stud to the guide pins. This type caming may be introduced when torque is applied to the head of the stud and a flat on the guide pin engages a stop on the support member causes. When additional torque is applied to the head the stud shifts in the axial opening in the ear and as the torque tightens the stud in the guide the head is clamped onto the ear and as a result the guide pin is retained in this shifted position. Since this fixing or attachment procedure is repeated for each guide pin sufficient binding can result which can effect the force required to slide caliper slides with respect to the support member during a brake application.
A primary object of the present invention is to provide a disc brake having guide pins that have a gap between a head on a stud and/or shoulder on a shaft with respect to an ear on a caliper that permit each guide pin to rotate to a centered aligned position in an axial opening in the ear on a caliper to reduce the introduction of frictional resistance to sliding movement during a brake application.
In more particular detail, the disc brake of this invention has a support member secured to a vehicle with spaced apart first and second bores for receiving corresponding first and second guide pins to position a caliper over a rotor. The caliper has an actuation section located on a first side of the rotor and an arm located on a second side of the rotor. The actuation section has an actuation bore therein for retaining a piston to define an actuation chamber and a bridge connected to an arm. A first friction member is associated with the piston and a second friction member is connected to the arm such that the first and second friction members are positioned on opposite sides of the rotor. The support member has first and second slots for receiving first and second projection on the first and second friction member. The caliper has a first ear that extends from the actuation section for receiving a first head of on a stud of the first guide pin and a second ear that extends from the actuation section for receiving a second head on as stud of the second guide pin. A function of the first guide pin in the first bore and the second guide pin in the second bore is to position the caliper over the rotor such that a parallel alignment is created between the first and second friction members and the rotor. In response to a desired braking of a wheel of the vehicle, the actuation chamber is presented with pressurized fluid from a source. The pressurized fluid on being presented to the actuation chamber acts on the piston to develop an actuation force that acts on the piston to move the first friction member in the first and second slots toward and into engagement with the rotor while at the same time creating a reaction force which acts on the actuation section and causes the caliper to slide on the first and second guide pins and move the second friction member in the first and second slots toward and into engagement with the rotor to effect a brake application. The first and second guide pins are characterized by a shaft with a cylindrical body having a first end and a second end. The first end has a first diameter section separated by a first shoulder from a second diameter section on the second end. A threaded axial bore extends from a face on the second end toward the first end. A stud or bolt has a shaft that extends from a head. The stud has a third diameter section that is separated by a second shoulder from a fourth diameter section that has threads thereon. The third diameter section has a length greater than a length of the first and second axial openings in the first and second ears. A resilient bushing is concentrically located on the third diameter section of the stud or bolt and is located in the axial opening of a corresponding first or second ears. The threads on the fourth diameter section are mated with the threaded axial bore of the cylindrical member and a torque is applied to rotate the head of the stud and bring the second shoulder into engagement with the face on the second end of the cylindrical member to securely fix the bolt to the cylindrical body of the shaft. Because of the difference in the length of the third diameter section and the width of the ear when the stud is secured to the cylindrical body a gap is defined between the head of the stud and/or the face of the cylindrical body and the ear such that the stud may freely rotate in the axial opening of the ear to permit the cylindrical body to be aligned in the bore of the support member without creating frictional resistance to movement of the caliper during a brake application. In addition, a dimensional difference or manufacturing tolerance between the third diameter section of the stud and the axial opening in the corresponding ear is greater than a dimensional difference between the first projections on the first and second friction members and the first slot in the support member and the second projections on the first and second friction members and the second slots in the support member such that during a brake application, resistive forces are transmitted through the first and second friction members into the support member rather than through the first and second guide pins.
An advantage of this disc brake results in the ease in which the guide pins are aligned in corresponding first and second bores in a support member to maintain a caliper in a desired alignment with a rotor and thereby reduce the introduction of caming frictional forces during a brake application.
An object of this invention is to provide a disc brake assembly with guide pins which become self-aligning with bores in a support member during a brake application.